Metallurgical composition embodying hard metal carbides, and method of making

ABSTRACT

A hard wear resistant metallurgical composition, particularly a sintered composition, utilizing hard metal carbides in which the composition can readily be formulated so as to be ferromagnetic or non-ferromagnetic. By non-ferromagnetic, hereinafter referred to as non-magnetic, a material is referred to which has magnetic permeability near unity and which is lacking in the ability to become magnetized or to exhibit induced magnetism, namely, a material with 0 oersted coercive force. The composition is, in general, a combination of tungsten, titanium, nickel and carbon, but may comprise other elements including chromium. In making the composition, tungsten carbide (WC) is admixed by milling with nickel (Ni) and titanium (Ti) and sintered. The titanium can react with carbon from the tungsten carbide and the released tungsten can alloy with nickel to form a tough binder. The characteristics of the end product can be tailored by controlling the proportions of the various components of the composition, including adjustment of the amount of titanium added to the mixture. The end product can, in this manner, be made magnetic or nonmagnetic, if desired, without losing the desirable characteristics of strength, hardness and wear resistance.

United States Patent [1 1 Nemeth et a1.

[ 1 Nov. 11, I975 1 1 METALLURGICAL COMPOSITION EMBODYING HARD METAL CARBIDES, AND METHOD OF MAKING [75] Inventors: Bela J. Nemeth; Alden M.

Burghardt, both of Greensburg. Pa.

[73] Assignee: Kennametal Inc., Latrobe. Pa.

[221 Filed: June 20. 1973 {21] Appl. No.: 371,598

3.510.276 5/1970 Dawihl et a1 3.756.787 9/1973 DeLange et al.

3.762.919 10/1973 Daniels 75/204 FOREIGN PATENTS OR APPLICATIONS 45-13212 5/1970 Japan 75/203 Primal EmminerBenjamin R. Padgett Assistant E.rmninerB. H. Hunt Armrner, Agent, or Firm-Melvin A. Crosby [57] ABSTRACT A hard wear resistant metallurgical composition. particularly a sintered composition. utilizing hard metal carbides in which the composition can readil be formulated so as to be ferromagnetic or non-ferromagnetic. By non-ferromagnetic. hereinafter referred to as non-magnetic. a material is referred to which has magnetic permeability near unit and which is lacking in the ability to become magnetized or to exhibit induced magnetism, namely. a material with O oersted coercive force. The composition is. in general. a combination of tungsten. titanium. nickel and carbon. but may comprise other elements including chromium. ln making the composition. tungsten carbide (WC) is admixed by milling with nickel (Ni) and titanium (Ti) and sintered. The titanium can react with carbon from the tungsten carbide and the released tungsten can alloy with nickel to form a tough binder. The characteristics of the end product can be tailored by controlling the proportions of the various components of the composition. including adjustment of the amount of titanium added to the mixture. The end product can. in this manner. be made magnetic or nonmagnetic, if desired. without losing the desirable characteristics of strength. hardness and wear resistance.

15 Claims. 2 Drawing Figures US Patent Nov. 11, 1975 3,918,138

WT. 70 TI TO CHARGE AS A FUNCTION OF C CONTENT OF WC TO YIELD THE DESIRED WT./W IN THE BINDER FOR A W-C TI-IO WT. Ni MIXTURE ASSUME 0.8 MOLAR RATIO OF 0 TO Ti w/w+NI=25% m. Y METAL ADDITION 0.6 w/w+NI=2O 02 w/w NI IO/ WT. CARBON IN wc FIG-2 PARTIAL Ni-W PHASE DIAGRAM MAGNETIC c TRANsFORMATION O f 0 IO 20 ATOMIC W METALLURGICAL COMPOSITION EMBODYING HARD METAL CARBIDES, AND METHOD OF MAKING The present invention relates to metallurgical compositions embodying metal carbides, in particular, hard metal carbides, and is especially concerned with a composition that can be tailored as to characteristics including that of being nonmagnetic or magnetic while remaining hard and wear resistant.

Many hard wear resistant metallurgical compositions embodying hard metal carbides are known, and most thereof are quite satisfactory for the intended use. An application for hard wear resistant carbide materials in connection with which there has not, heretofore, been satisfactory materials are those uses in which the hard wear resistant material must be nonmagnetic.

For example, machines in which magnetic tapes are employed often require wear resistant guides and the like for supporting and guiding the tapesv Still other cases will suggest themselves in which a hard wear resistant, or structurally strong, member is required where magnetic interactions are undesirable and in these cases, also, nonmagnetic carbide materials would be highly useful.

While the metallurgical composition according to the present invention can, as will be shown, be made nonmagnetic, magnetic variations of the composition have also been found highly useful in places where the composition must be hard and wear resistant and/or noncorrosive and/or noncontaminating or where the material must be extremely hard as in connection with a tool composition.

With the foregoing in mind, a primary objective of the present invention is the provision of a metallurgical composition embodying hard metal carbides which has the possibility of being formulated so as to be non-mag netic but which will retain the desirable attributes of hard carbide metallurgical compositions.

Another object is the provision of a metallurgical composition of the nature referred to which can be so compounded prior to the formation thereof as to be either non-magnetic or magnetic when completed.

A still further object is the provision of a metallurgical composition embodying hard metal carbides which is satisfactory for use as a tool and which can be compounded to vary in magnetic properties at room temperature to the state of being non-magnetic.

BRIEF SUMMARY OF THE INVENTION The metallurgical composition according to the present invention is concerned primarily with tungsten, titanium, nickel, carbon compositions and to which may be added a certain amount of chromium and other carbides. The composition of the present invention can be compounded in such a manner as to be either non-magnetic or magnetic while still having the desirable characteristics of hard wear resistant cemented carbides.

The hard metal carbides, including tungsten carbide and titanium carbide, are non-magnetic so that a metallurgical composition embodying hard metal carbides can be made provided a suitable metal binder system is employed which is also non-magnetic.

A binder metal for a cemented carbide composition should be tough and should also wet the carbide. A nickel binder system is, thus, a preferred binder because nickel wets the carbide compounds and is tough.

Nickel, furthermore, although being itself ferromagnetic, can be alloyed as with tungsten, which is also non-magnetic, without undergoing a phase change upon heating or upon cooling from the liquid phase over a relatively broad alloying range and an alloy of this material can be selected which is non-magnetic. as defined in the Abstract.

When the more common binder metal. cobalt. is employed as a binder. and the composition is adjusted to be. or to approach being, non-magnetic. the binder phase of the composition becomes extremely brittle due to the formation of CO W C and the composition is, thus, defective for many uses, The present invention overcomes this objection by including titanium in the composition and employing nickel or nickel and chromium as the basic binder metal.

When titanium, tungsten carbide and nickel, with or without some chromium, are admixed in powder form, compacted and heated so that a liquid phase is formed containing W, C and some or all of the titanium in solution, then the carbon can associate itself with the titanium to form titanium carbide or a solid solution ofTiC with WC, or both, because the free energy of formation for forming TiC is more favorable than for forming WC. Thus, tungsten is freed during sintering to alloy with a binder metal or metals.

The mass balance is calculated so the stoichiometric excess W during sintering can alloy with the nickel and result in a magnetic or non-magnetic binder alloy. The carbon balance with respect to the titanium must take into account the non-stoichiometric nature of TiC as less than one carbon atom per titanium atom is sufficient to form titanium carbide.

Thus, by including titanium in the mixture, carbon is removed from the melt because of the affinity of titanium for the carbon, and an alloy of nickel and tungsten and/or titanium is formed during sintering. It has been found that a fairly wide range of compositions according to the present invention will result in the production of a nonmagnetic alloy having the same crystal structure as pure nickel, namely, face centered cubic.

While carbon deficient tungsten carbide can be employed with a nickel binder to yield a nickeltungsten alloy binder after sintering, extremely close control of the respective levels of nickel and carbon are required and an impractical control situation arises.

It has been found that small, less than 0.5 weight per cent, titanium metal additions as described herein very effectively inhibit grain growth during sintering and result in a fine grained structure and consequently improved strength.

A particular advantage of the present invention is to be found in the fact that, once the analysis of the WC component is ascertained to reveal the amount of carbon in the WC component, the amount of Ti to add to the composition can readily be calculated. Formulation and control are thus greatly simplified.

The exact nature of the present invention will become more apparent upon reference to the following specification giving specific examples and to the accompanying drawings in which:

FIG. 1 is a graph giving weight per cent titanium to charge FIG. 2 is a part of the nickel-tungsten phase diagram showing. in particular, the magnetic transformation characteristics of nickel-tungsten alloys.

DETAILED DESCRIPTION OF THE INVENTION:

The compositions according to the present invention can be compounded by closely analyzing each constituent for the carbon. oxygen. nitrogen and metallic impurities. The amount of Ti required to release the quantity of tungsten from the tungsten carbide to produce the nickel-tungsten alloy composition can then be calculated or determined experimentally In making the calculations, the tungsten level desired in the binder and the nickel content are established and the equations giving the desired amount of titanium. or tungsten. are solved.

FIG. 1 shows how much titanium to charge with tungsten carbide having the indicated total carbon content and negligible oxygen. nitrogen and metallic impurities. ln the graph. the weight of Ni in the composition is always It). The other 90% of the composition is made up of WC Ti. Thus. for example. at 1 wt. "/r Ti. there will be 89 wt. 72 WC. Each line of the graph shows the amount of Ti to be supplied to obtain the indicated weight 7r of W in the binder.

TABLE I Weight Titanium to charge to a 10 Wt. 7c Nickel balance tungsten carbide composition (the WC having 6.10 Wt. 92 carbon content and negligible impurities) to obtain the calculated 1O. 20. or 25 Wt. 7r W/(W Ni) in the binder alloy as a function of carburization of the titanium addition.

4 and help to further inhibit grain growth and also to stabilize the nonmagnetic properties when the composition is to be non-magnetic. Chromium has produced good results and for a 10 weight 7( nickel composition. a 1 weight I chromium level produced satisfactory results.

The chromium metal addtion is not essential to achieve non-magnetic properties. It can react with and take up some of the carbon by forming carbides of chromium. and it can also alloy with the nickel.

Titanium can be supplied in the form of powders of titanium metal. any alloy of titanium with nickel. not necessarily Ti Ni euthectic composition or as a hydride of titanium. The last mentioned form is preferred because it is less reactive than the pure metal and can be milled readilyv Also. it is less expensive than an alloy of titanium with nickel while. furthermore. the hydrogen that is evolved from titanium hydride during the early stages of sintering can be beneficial because it can be effective for reducing surface oxides. particularly those which form on nickel.

The non-magnetic capability of the type of composition disclosed herein is important but there are other applications for the cornsition wherein chemical inertness and strength and wear resistance are the principal characteristics desired.

Non-magnetic grades of the composition. as mentioned, are particularly useful for magnetic tape guides and the like. Both magnetic and non-magnetic grades of the composition are useful as cutting tools and the like and also as tools for use in glass making and the like where cobalt contamination is detrimental.

, ESL The following chart gives a number of examples of Calculated Wt. Atom f. Wt 1,; q. Ti m Rims, compositions. the irst five thereof being non-magnetic Nicks] W/(W Ni) Charge T1 35 grades and the last two being magnetic grades:

TABLE [I SUMMARY OF EXAMPLES (Composition Prior W in Binder Coercive to Sintcring) After Siritering Force. Ave. Transverse Hardness Exam Research Weight 2 Est. Wt. He Rupture Strength Rockwell ple Mix N6. Ni Ti Cr WC {W/(W-1-Ni-1-Cr1] Oersteds PSI A" 1 o 5153 10.0 0.7111) 0 Hal. 0 451 90.9 484 91.0 2 G 6015 9.9 0.55( 11 09901 Bal. 21 0 257 92.6 444 91.9 3 G 6016 10.0 0.94111 O 8111. 0 317 91.4 4 G 6023 9.3 0.5511) 1.99121 Bal. :1 0 22-1 91.0 399 92.3 5 G 6027 23.0 106(1) 1011:; Bal. :5 0 386 86.5 413 86.3 6 c 6009 10.0 0.56( 1) o Bal. 15 32-51; 377 90.6

447 90.1 7 o 601: 10.0 0.4713 0 Bal. 14 39-44 401 90.7 455 90.6

l l)Ti charged as hydride (ZlCr charged as Ni-Cr alloy (3)Ti charged as Ti l\i alloy m m 0,383 Oh The last two columns of the chart, the first of which 10 10 0.2411 0.7 gives transverse rupture strength, and the other of which gives hardness on the Rockwell A scale. have 1U 30 3 two values for each composition. The reason for this is :8 60 that the upper number of each pair is the value ob- 5 51 tained when the composition is compacted and vacuum 10 :5 1 :42 0.6 sintered and the second value is for a vacuum sintered 10 25 1.077 0.7 v m 0940 (L8 specimen sub ected to reheating in the presence of a 10 :5 0.231 0.9 high pressure mtert gas.

Chromium metal additions may be made to the composition. as will be explained more fully hereinafter.

In making any of the compositions referred to above. conventional milling procedures may be followed. A tungsten carbide lined mill with tungsten carbide milling media therein is preferably employed to avoid con- 3 tamination. This mixture is milled for about 4 to days and then processed in a conventional manner to arrive at a sintered end product.

Sintering may be accomplished at from about l350 to about [550 Centigrade for a period of about 0.25 to 2.0 hours at 0.02 to 0.75 Torr.

It will be understood that during sintering tungsten released from tungsten carbide by the capturing of the carbon by titanium, can form what is referred to as Eta phase in combination with nickel and carbon or, if the composition contains chromium, with chromium and carbon.

Such a phase might be represented as Ni W C. This material will not, if present in smalll amounts. detract from the physical or magnetic properties of the material and serves as a part of the binder of the sintered composition.

Modifications may be made within the scope of the appended claims.

What is claimed is:

1. A method of making a sintered carbide product which comprises milling together a mixture comprising a major part tungsten carbide, titanium, about 10 weight nickel, compacting the milled mixture, and sintering the compacted milled mixture to form the product, the said titanium being added to the mixture calculated in an amount to decarburize the tungsten carbide to a degree which will release tungsten to form an alloy with the nickel up to about 28 weight tungsten in the alloy.

2. The method according to claim 1 which includes adding at least a part of the titanium in the form of an alloy of titanium and nickel.

3. The method according to claim 1 which includes adding at least a part of the titanium in the form of titanium hydride.

4. The method according to claim 1 which includes adding about 1 weight chromium to the mixture.

5. The method according to claim 1 wherein the titanium charged in the starting composition is such that the calculated ratio W/(W Ni) in weight ranges from about 14 to 28 and the composition in non-magnetic.

6. The method of inhibiting grain growth during sintering in a powder metal compact which is formed from hard metal carbides and nickel which comprises adding about 0.05 to about 2.0 weight 7c Ti to the mixture from which the compact is formed.

7. A sintered cemented carbide product whose composition comprises tungsten carbide, titanium carbide and a binder alloy comprising tungsten-nickel in which the ratio of the tungsten in the binder alloy to the binder alloy is from 2 to 28 per cent by weight.

8. A product according to claim 7 that is non-ferromagnetic and has a ratio of tungsten in the binder alloy to the binder alloy of l5 to 28 per cent by weight.

9. A product according to claim 7 that has ferromagnetic properties and has a ratio of tungsten in the binder alloy to the binder alloy of less than 14 per cent by weight.

10. A product according to claim 8 in which the powders charged in the mixture before sintering are about the following percentages by weight:

Nickel 3.0 to 25.0

Titanium .05 to 2.0

Tungsten Carbide Balance 11. A product according to claim 8 in which the binder alloy further includes chromium.

12. A product according to claim 11 in which the powders are charged in the mixture before sintering in about the following percentages by weight:

Nickel 3.0 to 25.0

Titanium .05 to 2.0

Chromium 0.0 to 2.0

Tungsten Carbide Balance 13. A product according to claim 10 in which the titanium is supplied in the form of titanium hydride.

14. A product according to claim 10 in which the titanium is supplied in the form of an alloy with at least a portion of the said nickel.

15. A product according to claim 8 in which the binder alloy further includes un-reacted titanium and the calculated ratio of the tungsten in the binder alloy to the binder alloy is from l5 to 28 per cent by weight. l 

1. A METHOD OF MAKING A SINTERED CARBIDE PRODUT WHICH COMPRISES MILLING TOGETHER A MIXTURE COMPRISING A MAJOR PART TUNGSTEN CARBIDE, TITANIUM, ABOUT 10 WEIGHT % NICKEL, COMPACTING THE MILLED MIXTURE, AND SINTERING THE COMPACTED MILLED MIXTURE TO FORM THE PRODUCT, THE SAID TITANIUM BEING ADDED TO THE MIXTURE CALCULATED IN AN AMOUNT TO DECARBURIZE THE TUNGSTEN CARBIDE TO A DEGREE WHICH WILL RELEASE TUNGSTEN TO FORM AN ALLOY WITH THE NICKEL UP TO ABOUT 28 WEIGHT % TUNGSTEN IN THE ALLOY.
 2. The method according to claim 1 which includes adding at least a part of the titanium in the form of an alloy of titanium and nickel.
 3. The method according to claim 1 which includes adding at least a part of the titanium in the Form of titanium hydride.
 4. The method according to claim 1 which includes adding about 1 weight % chromium to the mixture.
 5. The method according to claim 1 wherein the titanium charged in the starting composition is such that the calculated ratio W/(W + Ni) in weight % ranges from about 14 to 28 and the composition in non-magnetic.
 6. The method of inhibiting grain growth during sintering in a powder metal compact which is formed from hard metal carbides and nickel which comprises adding about 0.05 to about 2.0 weight % Ti to the mixture from which the compact is formed.
 7. A sintered cemented carbide product whose composition comprises tungsten carbide, titanium carbide and a binder alloy comprising tungsten-nickel in which the ratio of the tungsten in the binder alloy to the binder alloy is from 2 to 28 per cent by weight.
 8. A product according to claim 7 that is non-ferromagnetic and has a ratio of tungsten in the binder alloy to the binder alloy of 15 to 28 per cent by weight.
 9. A product according to claim 7 that has ferromagnetic properties and has a ratio of tungsten in the binder alloy to the binder alloy of less than 14 per cent by weight.
 10. A product according to claim 8 in which the powders charged in the mixture before sintering are about the following percentages by weight: Nickel - 3.0 to 25.0 Titanium - .05 to 2.0 Tungsten Carbide - Balance
 11. A product according to claim 8 in which the binder alloy further includes chromium.
 12. A product according to claim 11 in which the powders are charged in the mixture before sintering in about the following percentages by weight: Nickel - 3.0 to 25.0 Titanium - .05 to 2.0 Chromium - 0.0 to 2.0 Tungsten Carbide - Balance
 13. A product according to claim 10 in which the titanium is supplied in the form of titanium hydride.
 14. A product according to claim 10 in which the titanium is supplied in the form of an alloy with at least a portion of the said nickel.
 15. A product according to claim 8 in which the binder alloy further includes un-reacted titanium and the calculated ratio of the tungsten in the binder alloy to the binder alloy is from 15 to 28 per cent by weight. 